Not only are hours spent in front of the television hours you'll never get back, they may be hours actually taken off your lifespan, researchers found.
In an analysis of Australian lifestyle data, every hour spent watching TV was estimated to lower life expectancy by nearly 22 minutes for those 25 and older, Dr. J. Lennert Veerman of the University of Queensland and colleagues reported online in the British Journal of Sports Medicine.
In fact, folks who sit in front of the tube for an average of six hours a day may lose nearly five years compared with those who don't watch TV, the researchers said.
These estimates are comparable to, if not higher than, those of other risk factors including tobacco use and obesity, Veerman and colleagues reported.
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Although Australian and U.S. guidelines "recommend no more than two hours of screen time per day" for children, they wrote, "with further corroborative evidence, a public health case could be made that adults also need to limit the time spent watching TV."
Much research has shown that sedentary behavior is associated with greater risk of death. Several studies have focused specifically on mortality risk associated with one specific sedentary behavior -- watching TV -- but its impact on life expectancy hasn't been studied, the researchers said.
So they constructed a life table model using data from the Australian Bureau of Statistics and the Australian Diabetes, Obesity, and Lifestyle study, which was begun in 1999 with 11,247 participants 25 and older.
In 2008, these participants watched almost 10 billion hours of TV, and the researchers estimated that these hours were associated with a loss of 286,000 life years that year alone.
Comparatively, tobacco use was estimated to cause a loss of 178,000 life years in 2008, not getting enough exercise led to 127,000 lost life years, and obesity took a toll of 109,000 life years, the researchers reported.
Those who spend a lifetime average of six hours per day in front of the tube are expected to live about five years less than those who watch no TV, Veerman and colleagues reported.
They noted that, without TV viewing, the life expectancy at birth of Australian men in 2008 would have been 1.8 years higher than observed; for women it would have been 1.5 years higher.
"If these [figures] are confirmed, and shown to reflect a causal association, TV viewing is a public health problem comparable in size to established behavioral risk factors," they wrote.
For instance, patients older than 50 in the Framingham Heart study who had low physical activity levels lost about 1.4 years of life compared with those who exercised moderately and lost 3.6 years compared with those who got lots of exercise.
Using life expectancy at age 50, the researchers said, similar losses in life expectancy might be associated with watching about 2.1 and 5.4 hours of TV per day.
They also noted that in the study population obesity led to a loss of 1.3 years for men and one year for women, which compared to the effects of watching 1.9 and 1.6 hours of TV per day.
Finally, lifelong smoking was associated with 4.3 years of life lost for men and 4.1 years for women, which equates to 6.0 and 6.4 hours of watching TV daily, they reported.
Veerman and colleagues noted that sociodemographic groups who have a high prevalence of TV viewing -- those with lower levels of education, those living outside of state capital cities, and the unemployed -- may be particularly at risk.
The effects in countries outside of Australia are likely to be comparable, they added, given the many hours spent watching TV and similarities in disease patterns in these places, they wrote.
Yet further study is needed, they cautioned, to confirm life years lost and to specify the link between TV watching and death.